1. Field of the Invention
The present invention relates generally to scanning probe microscopy and, more particularly, to the system comprising control software that is used for operating the SPM. In accordance with one embodiment of the present invention, control software is disclosed that automates many of the steps required for obtaining a scanning probe microscopy image, thus substantially reducing the level of expertise required to operate a scanning probe microscope (SPM).
2. Description of the Prior Art
In an SPM, a sharp probe is scanned over a surface of a sample in a raster scan motion while the probe is maintained in a predetermined relationship to the surface. A sensing system, together with a feedback circuit and electromechanical transducer, is used to maintain the predetermined relationship between the probe and surface. A three-dimensional image of the surface may then be created by displaying the motion of the probe on a display such as a computer screen. FIG. 1 illustrates the primary components of a scanning probe microscope stage and control system.
The most commonly used type of SPM is the atomic force microscope (AFM). In an AFM, the relationship between the probe and surface of the sample is established using a force sensor comprising the sensing system. The probe is raster scanned in the XY plane, and the Z position of the probe is controlled by the sensing system together with a feedback circuit and an electromechanical transducer. The force sensor in an AFM can be a light lever design, or may be a quartz crystal sensor.
The stages of an SPM typically include a series of coarse translation mechanisms for moving the sample large distances, several millimeters, along the X, Y, and Z axes. Fine translation devices, typically piezoelectric elements, are also included for moving the probe along the X, Y, and Z axes during the imaging operation. Additionally, the SPM includes an optical microscope to facilitate locating features for scanning and for assisting in the motion of the probe as it is moved towards a sample's surface.
Practical operation of an SPM requires the control of all of the stage functions. The parameters that must be controlled include:
x raster—Size, Rate, Frequency
y raster—Size, Rate, Frequency
z feedback—Setpoint, PID parameters, bandwidth
Z Motion Control—Rate, Resolution
XY Motion Control—Rate, Resolution
Video Optic—Zoom, Focus
The first SPM, such as the scanning tunneling microscope (STM), used analog electronics to control all of the microscope functions. The human interface to the microscope was a series of knobs and buttons. Although this first approach was functional, it required an expert with an in-depth understanding of the microscope's design to operate.
With the advent of tabletop, affordable, personal computers, the control of scanning probe microscopes was converted to computer control. In such systems, a computer interface electronic unit comprised of analog-to-digital converters, digital-to-analog converters, and TTL logic were used in conjunction with “control software” for the microscope's control, as shown in FIG. 2.
The “control software” is used for controlling all of the scanning and stage functions described above. Initially, the “control software” simply replaced the analog control of the SPM. Over the past five to ten years, two software designs were created for SPM control.
In the first design, the control parameters can be accessed through a series of display screens. At any point, one of the display screens can be opened and a parameter changed. This type of control software is very powerful, but requires the operator to have a detailed knowledge of the microscope's operation.
In the second design, a menu is used that presents the steps required for obtaining a topographic image. FIG. 3 shows an example of this software design. This approach simplifies the operation of the SPM; however, it still requires the operator to have a substantial understanding of the microscope's operation to successfully measure topographic images.